One of the goals of the Consortium for the Integrative Neuroscience Initiative on Alcoholism is to elucidate the neurobiological mechanisms underlying various aspects of neuroadaptation to alcohol. This developmental grant application proposes the use of a novel approach to tease apart the molecular bases of neuroadaptation. Ethanol enhancement of serotonin-3 (5-HT3) receptor function is expressed in the form of a parallel sinistral shift of the 5-HT concentration-response curve. In contrast to ethanol, competitive antagonists competing with agonists at these receptors shift agonist concentration-response curves to the right, in a parallel manner. Mutations of a number of amino acids of 5-HT3 receptor subunits alter serotonin EC50s. Mutations resulting in sinistral shifts of neurotransmitter concentration-response curves thus mimic the effects of ethanol administration on wild-type receptors, while mutations that shifts the serotonin concentration-response curve to the right mimic the effect of 5-HT3 receptor antagonists such as ondansetron on wild-type receptors. Our first specific aim is to identify single amino-acid mutants of the 5-HT3 receptor that significantly shift serotonin concentration-response curves to either the left or right. These mutants will thus mimic the functional effects seen when ethanol or ondansetron, respectively, are applied to 5-HT3 receptors. Once the appropriate mutants are identified, we propose to create knock-in mice bearing the mutated 5-HT3 receptors identified in the first aim. It is hypothesized that knocking in the mutant receptor that produces a right- shifted serotonin concentration-response curve will result in a mouse that consumes less alcohol, because the functional effects of the mutation will be the same as those produced by the chronic administration of ondansetron. In contrast, a mouse bearing a 5-HT3 receptor mutated to produce a leftward shift in its serotonin concentration-response curve might drink more alcohol.